1. Field Of The Invention
The present invention generally relates to dielectric fluids used in capacitors, and in particular, two such fluids as include epoxide compounds.
2. Statement Of The Prior Art
Epoxides have been used as acid scavengers in dielectric fluids for many years. Prior to the banning of the use of polychlorinated biphenyls, epoxides were used in small amounts therewith to reduce acidity and related dielectric failure. After the banning of polychlorinated biphenyls, many alternatives were sought as a replacement for PCBs. Various suitable and quasi suitable compounds were found for replacing PCBs and with the experiments were performed to determine if epoxides would also be useful with these compounds as an acid scavenger. In many cases, it was found that epoxides did indeed continue to act as acid scavengers when used in small amounts. One such compound currently used as a dielectric fluid and which enjoys the benefits of small amounts of epoxide additive is dioctylphthalate. Another such suitable dielectric compound is a mixture of phenylxylyl ethyne and an organic phosphorous compound such a phosphate or phosphite. This combination is described in U.S. Pat. No. 4,053,941 along with the various epoxide additives, which are used in amounts varying between 0.5 and 5% by weight of the combined mixture. Generally, the organic phosphorous compound discussed therein was necessary for improving the dielectric constant of the fluid as the dielectric constant of the phenylxylyl ethyne was generally of too low a value to be of practical usefulness in capacitor construction.
Generally, if a dielectric constant is too low, the dielectric will break down under electrical stress more easily than a dielectric having a higher dielectric constant. In order to use a compound having a low dielectric constant as a dielectric, the electrical stress under which it was placed would have to be severely limited, or in the case of a capacitor, the spacing between electrodes would have to be made too large for practical volumetric efficiency of the capacitor. Thusly, it is preferred that mixtures to be used as dielectric fluids in capacitors have high values of dielectric constant in order to improve the volumetric efficiency and electrical stress characteristics of capacitors constructed therewith.